The present invention relates to a brake rubber hose used in the brake of an automobile. More specifically, it relates to an ultralow expansion brake rubber hose having extremely low expansion at an initial pressure and production method thereof.
In the hydraulic brake of an automobile, the force exerted on a brake pedal is converted into a fluid pressure by a master cylinder, and the fluid pressure is carried to each wheel cylinder through a brake rubber hose. A conventional brake rubber hose comprises a rubber tube and a reinforcing layer formed by braiding. FIG. 3 is a perspective view of the brake rubber hose with portions thereof cut out. The brake rubber hose comprises an inner rubber tube 1 made of brake fluid-resistant ethylene-propylene-diene rubber (EPDM) or styrene-butadiene rubber (SBR), a first reinforcing layer 2 formed by braiding vinylon fibers as reinforcing fibers, an intermediate rubber layer 3 made of natural rubber (NR), EPDM or butyl rubber (IIR), a second reinforcing layer 4 formed by braiding vinylon fibers, and an outer rubber tube 5 made of EPDM or chloroprene rubber (CR).
A method for producing the brake rubber hose having the above constitution is as follows. Firstly, the inner rubber tube 1 is extruded around the perimeter of a long resin mandrel, and the first reinforcing layer 2 is braided on the external surface of the inner rubber tube 1. Then, the intermediate rubber layer 3 is extruded on the external surface of the first reinforcing layer 2 by an extruder or formed by winding a long rubber tape around the layer 2. When the layer 3 is formed by winding the rubber tape around the layer 2, the second reinforcing layer 4 is braded on the tape while the tape is wound around the layer 2. Then, the outer rubber tube 5 is extruded around the perimeter of the second reinforcing layer 4. These rubber tubes are vulcanized together with the long mandrel. After vulcanization, the long mandrel is taken out by use of hydraulic pressure. Thereafter, the long rubber hose is cut to a predetermined length and used.
In recent years, along with the advance of engine technology, road conditions are improved, the speed of a vehicle is increased, whereby further attention is paid to the performance of a brake and the performance of the brake is required to meet strict standards. Particularly, a braking capability and a feeling of braking are required to meet strict standards. Within a range of pressures exerted on the brake rubber hose, low pressures of 0 to 2.94 MPa are related to the feeling of braking. The reason why the internal volume of the hose is expanded at such low pressures is assumed to be not because the fibers constituting the reinforcing fiber layers in the structure of the hose extend elastically, but because the braided reinforcing fibers slip against each other. It is also assumed that the looseness in the braided fibers has a serious effect on the expansion of the internal volume.
Particularly, the expansion of the internal volume is controlled by the first reinforcing layer 2. Thus, to prevent the slippage between the braided reinforcing fibers, a method has heretofore been employed that comprises bonding and fixing braided reinforcing fibers (vinylon fibers) on the external surface of the inner rubber tube 1 by an adhesive.
However, the method of bonding and fixing reinforcing fibers on the external surface of the inner rubber tube by an adhesive has the following problems. That is, as the adhesive, a rubber-based solution-type vulcanization adhesive is generally used. Since the rubber-based solution-type vulcanization adhesive contains a solvent, it must be dried for a given time period after applied to the inner rubber tube 1. For this reason, the first reinforcing layer 2 cannot be braided immediately and continuously after the rubber-based solution-type vulcanization adhesive is applied to the inner rubber tube 1.
Further, although the reinforcing fibers are bonded to the inner rubber tube, the reinforcing fibers themselves are not always bonded to each other. For this reason, the reinforcing fibers of the first reinforcing layer 2 are displaced with the inner rubber tube 1 while stuck on the inner rubber tube, so that the mutual slippage between the reinforcing fibers of the first reinforcing layer 2 cannot be prevented completely. Therefore, a brake rubber hose having small expansion cannot be obtained by simply bonding the reinforcing fibers of the first reinforcing layer 2 to the inner rubber tube.
The present invention has been invented under the above present circumstances. It is an object of the present invention to provide the following target brake rubber hose and production method thereof.
It is an object of the present invention to provide a brake rubber hose which is completely free of the mutual slippage between the reinforcing fibers of the first reinforcing layer, and production method thereof.
It is another object of the present invention to provide an ultralow expansion brake rubber hose and production method thereof by preventing the mutual slippage between the reinforcing fibers of the first reinforcing layer completely.
To achieve the above objects, the present invention is constituted as follows. That is, the ultralow expansion brake rubber hose according to the present invention comprises an inner rubber tube, a first reinforcing layer, a second reinforcing layer and an outer rubber layer. The ultralow expansion brake rubber hose is characterized in that a thermosetting resin which is set at vulcanizing temperatures is caused to penetrate the reinforcing fibers constituting the first reinforcing layer and then cured by vulcanization to turn the first reinforcing layer into a solid cured layer.
The above inner rubber tube can be made of EPDM that a brake fluid can hardly penetrate, and the outer rubber layer can also be made of EPDM. As the reinforcing fibers constituting the first reinforcing layer and the second reinforcing layer, vinylon fibers can be used. As the thermosetting resin caused to penetrate the reinforcing fibers, a melamine resins or a phenol resin can be used.
Further, a method for producing the ultralow expansion brake rubber hose having the above constitution comprises the continuous steps of braiding the first reinforcing layer on the inner rubber tube, immersing the reinforcing fibers constituting the first reinforcing layer in a thermosetting resin solution capable of penetrating the reinforcing fibers and having low viscosity to cause the thermosetting resin solution to penetrate the reinforcing fibers, braiding the second reinforcing layer, and extruding the outer rubber tube on the external surface of the second reinforcing layer. In the step of causing the above thermosetting resin solution to penetrate the reinforcing fibers, a bath containing a thermosetting resin solution capable of penetrating the reinforcing fibers and having low viscosity is provided, and the reinforcing fibers are forcibly immersed in the bath to cause the thermosetting resin solution to penetrate the reinforcing fibers. Further, it is preferable to carry out the step of curing the inner rubber tube, the thermosetting resin and the outer rubber tube by vulcanization subsequently to the step of extruding the outer rubber tube.
In the present invention, since the first reinforcing internal layer is turned into a solid cured layer by causing the thermosetting resin to penetrate the reinforcing fibers of the first reinforcing layer and curing the thermosetting resin, the mutual slippage between the reinforcing fibers of the first reinforcing layer which controls the expansion of the internal volume when a pressure is applied can be prevented completely, and expansion can be held low. Therefore, a brake rubber hose which is excellent in a feeling of braking and durability can be obtained. When the thermosetting resin is applied only to the surface of the first reinforcing layer and cured after the first reinforcing layer is braided on the inner rubber tube, the thermosetting resin cannot fully penetrate the first reinforcing layer to reach the surface of the inner rubber tube and the coating resin layer is limited in thickness, so that the reinforcing fibers cannot be cured completely. Consequently, a mutual slippage occurs between the reinforcing fibers, and displacement between the reinforcing fibers when a pressure is applied cannot be prevented. The first reinforcing layer can be turned into a cured layer when the thermosetting resin penetrates the inside of the reinforcing fibers.
Further, since the external surface of the first reinforcing layer cured by the thermosetting resin has high abrasion resistance, an intermediate rubber layer for preventing abrasion between the first reinforcing layer and the second reinforcing layer is not needed. In addition, unlike the prior art, since a rubber-based solution-type vulcanization adhesive containing a solvent is not used, a production process in which the extrusion of the inner rubber tube and the braiding of the first reinforcing layer are performed continuously can be adopted, and such an environmental problem as air pollution caused by the evaporation of the solvent does not occur.